The use of manifolds in injection molding apparatuses to transfer melt from a melt source to one or more mold cavities is well known. In many instances, it may be desired to mix a melt flow in a manifold, due to the configuration of a runner in the manifold, the composition of the melt flow and/or other parameters relating to the injection molding application. For example, it may be that a mixing device is used for the balancing of a manifold, to prevent certain mold cavities from receiving melt at a higher temperature and at a higher pressure than other mold cavities.
A well known device for mixing melt flow in a runner of a manifold is a static mixer. An example of such a mixer is disclosed in European Patent Application No. 88108394.3 (Halar et al.). Halar et al. discloses a mixer which is positioned in a runner, and which has a number of radially extending vanes. The vanes are twisted, and thus interrupt and twist a melt flow to cause mixing of the melt flow.
Another mixing device is disclosed in U.S. Pat. No. 4,123,496 (Gallizia et al.). Gallizia et al. discloses a mixing device for the purpose of balancing a manifold. The mixing device is configured to rearrange strata of a shear heated melt flow, so that strata that are hotter are mixed with strata that are colder. The mixing device divides a melt flow in a runner into a number of smaller melt channels, which reposition the portions of the melt flow, and then discharge the melt flow back into the runner.
All such static mixing devices include a number of dead zones, where melt flow is inhibited, and which are difficult to clean, during a changeover from one melt type to another. Furthermore, such mixing devices represent a relatively large pressure drop for a melt flow.
U.S. Pat. No. 6,077,470 (Beaumont) discloses another way of balancing a manifold, whereby the runners are configured to reorient a melt flow, so that the melt flow divides evenly at a split. Beaumont's device does not mix a melt flow, but instead reorients it so that non-uniformities in the melt flow will divide evenly at a split.
U.S. Pat. No. 5,683,731 (Deardruff et al) discloses a redistributor device for dividing a melt flow evenly upstream from an X-type split, where the melt is ultimately split into four downstream runners. The redistributor device has four internal passages which draw melt from different parts of a non-uniform melt flow and redistributes them so that non-uniformities are divided evenly in each of the downstream runners. The device of Deardruff et al. has several drawbacks. The internal passages are relatively difficult to clean. Furthermore, the device does not mix a melt flow, but instead divides it into portions and redistributes the portions, so the downstream melt flows may not be uniform themselves.
A continuing need therefore exists for new devices for the mixing of a melt flow and for the balancing of a manifold in an injection molding apparatus.